Liquid-phase growth apparatus and method

ABSTRACT

A liquid-phase growth apparatus for growing a crystal on a substrate includes a crucible containing a solution that contains a raw material for forming the crystal, and a substrate holder for vertically holding the substrate. The substrate holder includes connectors, a receiving component, and a push component. The receiving component and the push component are opposite to each other and are connected by the connectors. The push component holds an upper portion of the substrate while the receiving component holds a lower portion of the substrate. The substrate holder containing the vertically held substrate is dipped into the solution. The receiving component ascends with buoyancy in the solution contained in the crucible, so that the substrate is now held securely and prevented from cracking due to thermal expansion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid-phase growth apparatusfor growing a crystal on a seed substrate that is vertically held with asubstrate holder and is dipped in a solution containing a solute (rawmaterial) for forming the crystal in a crucible, and to a liquid-phasecrystal growth method using the apparatus.

[0003] 2. Description of the Related Art

[0004] Liquid-phase growing is known as a method for preparing ahigh-quality monocrystalline thin film at relatively low temperature.Unfortunately, in a dipping process that includes dipping a substrateheld with a substrate holder in a solution, films are deposited on twofaces of the substrate.

[0005] Some methods are proposed for depositing a thin film only on oneface of the substrate. For example, a substrate is placed on a platinumholder and fixed with fixing claws to inhibit growth of the film on therear face of the substrate. In another proposed method, two substratesthat are in close contact with each other at the rear faces are dippedin a solution to facilitate crystal growth on the front faces of thesubstrates.

[0006] In liquid-phase crystal growth by general dipping, the substrateis held to the substrate holder horizontally or at a slight tilt anglefrom the level line. In such a case, a thicker film is deposited on thedown face of the substrate rather than the upper face. In particular,this tendency is noticeable in liquid-phase growth of a silicon crystalfrom an indium solvent since the specific gravity of the material(silicon) for forming the crystal is considerably lower than that of thesolvent.

[0007] When the substrate is vertically held in a general dippingmethod, films may be formed on two faces of the substrate or thesubstrate may be cracked by thermal expansion.

SUMMARY OF THE INVENTION

[0008] The present invention provides a liquid-phase growth apparatusand a method that can restrain cracking by thermal expansion of avertically held substrate dipped in a solution.

[0009] The present invention preferably provides a liquid-phase growthapparatus and a method hat can suppress crystal growth on the rear faceof a substrate.

[0010] According to a first aspect of the present invention, aliquid-phase growth apparatus for growing a crystal on a substrateincludes a crucible containing a solution that contains a raw materialfor forming the crystal; and a substrate holder for vertically holdingthe substrate. The substrate holder includes connectors; and a receivingcomponent and a push component which are opposite to each other and areconnected by the connectors. The push component holds an upper portionof the substrate while the receiving component holds a lower portion ofthe substrate. The receiving component ascends with buoyancy in thesolution contained in the crucible.

[0011] Preferably, the push component and the receiving component havegrooves for holding two ends of the substrate.

[0012] Preferably, each of the grooves has inclined planes for guidingeach end of the substrates.

[0013] Preferably, the push component is vertically movable and holdsthe substrate together with the receiving component by own weight of thepush component when the substrate is not dipped in the solution.

[0014] Preferably, the receiving component has a window that facilitatescirculation of the solution.

[0015] Preferably, the substrate holder holds a plurality of thesubstrates arranged radially at a predetermined interval in thecircumferential direction of the crucible.

[0016] A plurality of the receiving components and a plurality of pushcomponents may be alternately connected in the vertical direction withlong connectors.

[0017] According to a second aspect of the present invention, there isprovided a liquid-phase growth method for growing a crystal on asubstrate that is dipped in a solution containing a raw material forforming the crystal in a crucible. The method includes holding asubstrate vertically between a receiving component and a push componentthat are connected with connectors, wherein the push component and thereceiving component hold the substrate by buoyancy of the receivingcomponent when the substrate is dipped into the solution.

[0018] Preferably, two substrates are put into contact with each otherat the rear faces thereof or with a face of a dummy plate, and the twosubstrates or the substrate and the dummy plate are held between thepush component and the receiving component.

[0019] Preferably, the two substrates or the substrate and the dummyplate are put into close contact with each other by buoyancy of thereceiving component.

[0020] Preferably, the push component is vertically movable andvertically holds the substrate together with the receiving component byown weight of the push component when the substrate is not dipped in thesolution.

[0021] According to a third aspect of the present invention, aliquid-phase growth apparatus for growing a crystal on a substrateincludes a crucible containing a solution that contains a raw materialfor forming the crystal; and a substrate holder for vertically holdingthe substrate. The substrate holder includes connectors; and a receivingcomponent and a push component which are opposite to each other and areconnected by the connectors. The push component holds an upper portionof the substrate while the receiving component holds a lower portion ofthe substrate. The receiving component has a V groove at a surfaceopposite to the push component, and the push component has an inverted Vgroove at a surface opposite to the receiving component, the V groovefacing the inverted V groove, the receiving component holding a loweredge of the substrate while the push component holds an upper edge ofthe substrate. The receiving component is loosely connected to the pushcomponent with the connectors so as to be vertically movable so that thereceiving component comes down by the own weight when the substrateholder is not dipped in the solution and comes up by buoyancy thereofwhen the substrate holder is dipped in the solution.

[0022] Preferably, the total specific gravity of movable componentsincluding the receiving component is smaller than that of the solutionin the crucible.

[0023] Preferably, the push component is vertically movable and hasdownward force by own weight to hold the substrate vertically with thereceiving component when the substrate is not dipped in the solution.

[0024] According to the present invention, when the substrate is heatedor vertically dipped into the solution it will not crack by thermalexpansion in the preheating process or in the dipping process in thesolution. That is, the thermal expansion of the substrate is absorbed bythe tolerance of the vertically movable push component.

[0025] Since the two substrates or the substrate and the dummy plate areput into close contact in the solution, film deposition does not occuron the rear face(s) of the substrate(s), irrespective of verticalarrangement of the substrate(s) in the solution.

[0026] Furthermore, the push component presses the substrate by its ownweight when the substrate is not dipped into the solution. Thus, thesubstrate can be easily put in position. Furthermore, the push componentputs the substrate into close contact with another substrate or a dummyplate when these are dipped into the solution. Thus, the solution doesnot enter the rear face(s) of the substrate(s).

[0027] In this apparatus, the solution is uniformly circulated in thecrucible. Thus, the film deposited on the substrate has a uniformthickness.

[0028] Other features and advantages of the present invention will beapparent from the following description of taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic cross-sectional view of a substrate holderunit in a liquid-phase growth apparatus according to an embodiment ofthe present invention;

[0030]FIG. 2 is a schematic cross-sectional view of a substrate holderunit when substrates are dipped in a solution contained in a crucible inan embodiment of the present invention;

[0031]FIG. 3 is a schematic cross-sectional view of a substrate holderunit in a liquid-phase growth apparatus according to another embodimentof the present invention;

[0032]FIG. 4 is a schematic cross-sectional view of a substrate holderunit when substrates are dipped in a solution contained in a crucible inan embodiment of the present invention;

[0033]FIG. 5 shows a vertical triple arrangement of the substrate holderunits shown in FIGS. 3 and 4;

[0034]FIG. 6 is a top view of the receiving component shown in any oneof FIGS. 1 to 4:

[0035]FIG. 7 is a top view of a receiving component having a window of aliquid-phase growth apparatus according to another embodiment; and

[0036]FIG. 8 is a top view showing a radial arrangement of substrates ona receiving component of a liquid-phase growth apparatus according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The preferred embodiments of the present invention will now bedescribed with reference to the drawings. However, the present inventionis not limited to these embodiments and may include variousmodifications.

[0038]FIG. 1 is a schematic cross-sectional view of a substrate holderunit 20 in a liquid-phase growth apparatus according to an embodiment ofthe present invention. The substrate holder unit 20 primarily includes apush component 1 and a receiving component 2 that are arranged inparallel at a predetermined distance. The substrate holder unit 20further includes connectors 3 that connect the push component 1 and thereceiving component 2. The receiving component 2 has a plurality of Vgrooves 8 b on its top face. The push component 1 has a protrudingsegment 9 at its bottom. The protruding segment 9 has a plurality ofinverted V grooves 8 a on its bottom face, the inverted V grooves 8 afacing the respective V grooves 8 b. Two substrates 7 that are in closedcontact with each other at the rear faces are vertically held between aninverted V groove 8 a and the corresponding V groove 8 b. The substrates7 may be slightly tilted.

[0039] The connectors 3 are vertically fixed at the two ends of thereceiving component 2. Each connector 3 has a screw 4 at the top. Thepush component 1 has two opening (not shown) at the both ends. Eachconnector 3 extends through the corresponding opening of the pushcomponent 1 and is fixed with a screw nut 5. The connectors 3 may befixed with any fixing bracket other than the screw nuts 5, for example,with pins.

[0040]FIG. 1 shows an arrangement of the substrates 7 beforeliquid-phase growth. It is important that the screw nuts 5 are notcompletely tightened to hold the substrates, but are slightly loosenedsuch that the receiving component 2 can slightly moves vertically andthat the substrates 7 are held with slackness and do not detached fromthe inverted V grooves 8 a. A vertically movable shaft 6 is fixed to theupper center of the push component 1. After the substrates 7 are placedbetween the inverted V grooves 8 a and the V grooves 8 b, the shaft 6moves vertically to dip the substrates 7 into a solution forliquid-phase growth. In a typical liquid-phase growth method, thesubstrates 7 are preliminarily heated and then dipped into the solution.Even if the substrates 7 thermally expand, the allowance of the invertedV grooves 8 a prevents the substrates 7 from cracking.

[0041]FIG. 2 is a schematic cross-sectional view of the substrate holderunit 20 when the substrates 7 are dipped in a solution 11 contained in acrucible 10. As shown in FIG. 2, the substrates 7 are held between thepush component 1 and the receiving component 2 while the shaft 6 ismoved downward to dip the substrates 7 into the solution 11. Thereceiving component 2 and the connectors 3 are formed of a material ormaterials that have a smaller specific gravity than that of the solution11. Thus, these components ascend and push up the substrates 7 bybuoyancy in the solution 11. In this situation, the two lappedsubstrates 7 are tightly fixed to the corresponding inverted V groove 8a, so that the rear faces of these substrates 7 are not exposed to thesolution 11. The V grooves 8b and the inverted V grooves 8 a may bereplaced with grooves and inverted grooves having inclined planes thatcause contact force between the lapped substrates 7.

[0042] In this liquid-phase growth apparatus, adequate buoyancy actingon the receiving component 2 maintains close contact of the lappedsubstrates 7 even if the substrates 7 expand or contract in thesolution.

[0043] preferably, the solution 11 is stirred without rotation of thesubstrate holder unit 20 to maintain the stable vertical arrangement ofthe substrates 7. A stirring impeller 12 provided on the bottom of thecrucible 10 rotates to circulate the solution 11 vertically in thecrucible 10.

[0044]FIG. 3 is a schematic cross-sectional view of a substrate holderunit 20 in a liquid-phase growth apparatus according to anotherembodiment of the present invention. A push component 1 is not fixed toa shaft 6 and thus is vertically movable within a predetermined length.More specifically, screws 4 of connectors 3 extend through openings (notshown) at both ends of the push component 1 and openings (not shown) atboth ends of a fixing plate 6 a, and are fixed to the fixing plate 6 awith screw nuts 5. A vertically movable shaft 6 is fixed to the uppercenter of the fixing plate 6 a.

[0045] As described above, it is important that the screw nuts 5 are notcompletely tightened, but are slightly loosened such that the pushcomponent 1 and the receiving component 2 can slightly move vertically.In this embodiment, the push component 1 presses the substrates 7 by itsown weight when the substrates 7 are not dipped into a solution 11.Thus, the substrates 7 can be easily put in position. Furthermore, theallowance and tolerance of the push component 1 prevents the expandedsubstrates 7 from cracking.

[0046]FIG. 4 is a schematic cross-sectional view of a substrate holderunit 20 when substrates 7 are dipped in a solution 11 contained in acrucible 10, in accordance with another embodiment of the presentinvention. A receiving component 2 and connectors 3 ascend and push upthe substrates 7 together with a push component 1 by buoyancy in thesolution 11. The substrates 7 are always held between inverted V grooves8 a and V grooves 8 b both when the substrates 7 are dipped and notdipped in the solution 11, so that the two lapped substrates 7 are inclose contact with each other.

[0047] In the substrate holder unit 20 of the liquid-phase growthapparatus according to the present invention, components that are dippedin the solution are composed of materials having a specific gravitysmaller than that of the solution and having high heat resistance.Examples of such materials include quartz and graphite carbon. The widthand the depth of the inverted V grooves 8 a and the V grooves 8 b may bedetermined depending on the thickness of the substrates 7. The pushcomponent 1 may have inverted grooves, in place of the inverted Vgrooves 8 a of the protruding segment 9. Alternatively, grooves may beformed on a bank plate provided on the receiving component 2, in placeof the V grooves 8 b on the receiving component 2. The bank platecorresponds to the protruding segment 9.

[0048] In the above embodiments, the rear faces of the two substrates 7are in contact with each other. Alternatively, one substrate 7 may beput into contact with a dummy plate having substantially the same size.The dummy plate may be composed of, for example, quartz or graphitecarbon. Alternatively, two substrates may be placed on the both faces ofthe dummy plate.

[0049]FIG. 5 shows a triple arrangement of the substrate holder unitsshown in FIGS. 3 and 4. Receiving components 2 a and 2 b also functionas push components of the lower stages. Long connectors 3 are verticallyfixed to a receiving component 2 c at the bottommost stage. Eachconnector 3 extends through openings (not shown) of the receivingcomponents 2 a and 2 b, a push component 1, and a fixing plate 6 a, andis fixed to the fixing plate 6 a with a screw nut 5 tightened around ascrew 4. The connectors 3 may be detachable from the receiving component2 c.

[0050]FIG. 6 is a top view of the receiving component 2 shown in FIGS. 1to 4. The V grooves 8 b that are tailored to the size of the substratesare arranged in parallel on the surface of the square or rectangularreceiving component 2.

[0051]FIG. 7 is a top view of the receiving component 2 according toanother embodiment. In this embodiment, V grooves 8 b are arranged tosupport only both ends of each substrate. The center of the receivingcomponent 2 is cut out to form a window 15. The window 15 facilitatesvertical circulation of the solution. Furthermore, the receivingcomponent 2 prevents overflow of the solution from the crucible when thesubstrates are dipped into the solution and significantly reduces thevolume of the solution that is carried away from the crucible when thesubstrates are pull out of the solution.

[0052]FIG. 8 is a modification of the receiving component 2 shown inFIG. 7. In this modification, substrates are disposed radially. When acylindrical crucible is used in the modification, the solution isuniformly circulated between these substrates.

[0053] The liquid-phase growth apparatus according to the presentinvention can be applied to liquid phase epitaxial (LPE) growth ofvarious materials. For LPE growth of magnetic garnet used inmagneto-optical devices, the solution 11 is a melt of PbO and B₂O₃ assolvents and raw garnet as a solute. For LPE growth of lithium niobateused in nonlinear optical devices, the solution 11 is a melt of LiO₂,Nb₂O₅, and V₂O₅. For LPE growth of GaAs, a group III-V compoundsemiconductor, used in oscillating devices or light-emitting devices,the solution 11 is a melt of Ga as a solvent, polycrystalline GaAs as asolute, and Si and the like as dopants. For LPE growth of Si used insemiconductor ICs and solar cells, the solution 11 is a melt of Sn, In,Al, or Cu as a solvent, Si as a solute (raw material), and B, Al, P, orAs as a dopant.

EXAMPLE

[0054] A nonlimiting example of the present invention will now bedescribed. The liquid-phase growth apparatus according to the presentinvention was used for forming a monocrystalline silicon thin film.Substrates were disposed radially as shown in FIG. 8.

[0055] Substrates 7 were p+ silicon substrates having a square shapewith a side of 125 mm and a thickness of 0.6 mm. Each silicon substratewas anodized to form a porous surface layer with a thickness of 12 μm.Rear faces of two substrates were put into close contact with bothsurfaces of a quartz square dummy plate with a side of 125 mm and athickness of 0.6 mm, and this substrate combination was placed into thesubstrate holder unit 20. The receiving component 2 was composed ofquartz and had a diameter of 350 mm and a thickness of 5 mm. Thereceiving component 2 had V grooves 8 b that supported 5 mm from eachend of the substrate combination. Each V groove 8 b had a width of 2.5mm and a cross-sectional angle of 60°. The V grooves 8 b were radiallyarranged at an interval of 4.5° to place 80 substrate combinationsradially.

[0056] Four receiving components were stacked as shown in FIG. 5 to hold640 substrates. A solution 11 containing 550 kg of indium and 5.5 kg ofgallium (solvents) was placed into a quartz crucible 10 with an innerdiameter of 400 mm and a depth of 600 mm, and 17.5 kg of silicon(solute) was saturated to the solution at 930° C. and the solution wascooled to 923° C. to form a supersaturated solution.

[0057] After the substrates 7 were annealed with hydrogen at 1,050° C.for 20 minutes, they were dipped into the solution 11. While thestirring impeller 12 in the crucible 10 was rotated at 10 rpm tocirculate the solution 11 vertically, the solution 11 was cooled at acooling rate of 2° C./min. Sixty minutes later, a monocrystallinesilicon film with a thickness of 80 μm was prepared.

[0058] While the present invention has been described with reference towhat are presently considered to be the preferred embodiments, it is tobe understood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A liquid-phase growth apparatus for growing acrystal on a substrate, comprising: a crucible containing a solutionthat contains a raw material for forming the crystal; and a substrateholder for vertically holding the substrate, the substrate holderincluding: connectors; and a receiving component and a push componentwhich are opposite to each other and are connected by the connectors,the push component holding an upper portion of the substrate, thereceiving component holding a lower portion of the substrate, whereinthe receiving component ascends with buoyancy in the solution containedin the crucible.
 2. The apparatus according to claim 1, wherein the pushcomponent and the receiving component have grooves for holding two endsof the substrate.
 3. The apparatus according to claim 2, wherein each ofthe grooves has inclined planes for guiding each end of the substrates.4. The apparatus according to claim 1, wherein the push component isvertically movable and hold the substrate together with the receivingcomponent by own weight of the push component when the substrate is notdipped in the solution.
 5. The apparatus according to claim 1, whereinthe receiving component has a window that facilitates circulation of thesolution.
 6. The apparatus according to claim 1, wherein the substrateholder holds a plurality of the substrates arranged radially at apredetermined interval in the circumferential direction of the crucible.7. The apparatus according to claim 1, wherein a plurality of thereceiving components and a plurality of push components are alternatelyconnected in the vertical direction with long connectors.
 8. Aliquid-phase growth method for growing a crystal on a substrate that isdipped in a solution containing a raw material for forming the crystalin a crucible, the method comprising: holding a substrate verticallybetween a receiving component and a push component that are connectedwith connectors, wherein the push component and the receiving componenthold the substrate by buoyancy of the receiving component when thesubstrate is dipped into the solution.
 9. The method according to claim8, wherein two substrates are put into contact with each other at therear faces thereof or with a face of a dummy plate, and the twosubstrates or the substrate and the dummy plate are held between thepush component and the receiving component.
 10. The method according toclaim 9, wherein the two substrates or the substrate and the dummy plateare put into close contact with each other by buoyancy of the receivingcomponent.
 11. The method according to claim 8, wherein the pushcomponent is vertically movable and vertically holds the substratetogether with the receiving component by own weight of the pushcomponent when the substrate is not dipped in the solution.
 12. Aliquid-phase growth apparatus for growing a crystal on a substrate,comprising: a crucible containing a solution that contains a rawmaterial for forming the crystal; and a substrate holder including:connectors; and a receiving component and a push component which areopposite to each other and are connected by the connectors, thesubstrate holder vertically holding the substrate, the push componentholding an upper portion of the substrate, the receiving componentholding a lower portion of the substrate, wherein the receivingcomponent has a V groove at a surface opposite to the push component,and the push component has an inverted V groove at a surface opposite tothe receiving component, the V groove facing the inverted V groove, thereceiving component holding a lower edge of the substrate while the pushcomponent holds an upper edge of the substrate, wherein the receivingcomponent is loosely connected to the push component with the connectorsso as to be vertically movable so that the receiving component comesdown by the own weight when the substrate holder is not dipped in thesolution and comes up by buoyancy thereof when the substrate holder isdipped in the solution.
 13. The apparatus according to claim 12, whereinthe total specific gravity of movable components including the receivingcomponent is smaller than that of the solution in the crucible.
 14. Theapparatus according to claim 12, wherein the push component isvertically movable and has downward force by own weight to hold thesubstrate vertically with the receiving component when the substrate isnot dipped in the solution.